debug info omitted for uninitialized variables

[Devang Patel <dpatel at apple dot com>]

This was discussed as part of bugzilla PR/21828. I have filed PR 23190.

$ cat t.c
static int foo;
int bar;
int main(void)
{
   foo += 3;
   bar *= 5;
   return 0;
}

$ xgcc -g  -O2 -o t t.c
$ cat gdbcmds
b main
ptype foo
ptype bar
p foo
p bar
$ gdb --batch -x gdbcmds t
Reading symbols for shared libraries ... done
Breakpoint 1 at 0x2d14: file t.c, line 6.
type = <unknown type>
type = <unknown type>
$1 = <unknown type>
$2 = <unknown type>

[ This was discussed in PR 21828 ]

>On Jul 22, 2005, at 4:43 PM, mark at codesourcery dot com wrote:
>
>First, your example was not the one in the original bug report.
>
>Second, you're using STABS, not DWARF-2.  I suspect the stabs debug
>generator, or the GDB stabs reader is not as good as DWARF.
>
>On GNU/Linux, GDB knows that "bar" has type "int".  It still doesn't
>know the type of "foo"; apparently too much of the debug  
information is
>optimized away.  But, that's some other problem -- perhaps in GDB
>itself.  The information is clearly there for it:
>
>        .uleb128 0x2    # (DIE (0x2d) DW_TAG_variable)
>         .ascii "foo\0"  # DW_AT_name
>         .byte   0x1     # DW_AT_decl_file
>         .byte   0x1     # DW_AT_decl_line
>         .long   0x38    # DW_AT_type
>         .uleb128 0x3    # (DIE (0x38) DW_TAG_base_type)
>         .ascii "int\0"  # DW_AT_name
>         .byte   0x4     # DW_AT_byte_size
>        .byte   0x5     # DW_AT_encoding


It seems this is related to order of cgraph_optimize() and writing  
globals. If globals are wrapped up  before emitting code then debug  
info. is not emitted for uninitialized globals, because DECL_RTL is  
not  set. C++ FE writes globals before doing cgraph_optimize(), but C  
FE optimizes first. This is why this is C specific only. This patch  
fixes this but it causes varpool-1.c test failure. With this patch,  
GDB know about foo as well as bar when DWARF is used.


Index: c-decl.c
===============================================================
====
RCS file: /cvs/gcc/gcc/gcc/c-decl.c,v
retrieving revision 1.677
diff -Idpatel.pbxuser -c -3 -p -r1.677 c-decl.c
*** c-decl.c    19 Jul 2005 20:19:09 -0000      1.677
--- c-decl.c    28 Jul 2005 19:22:47 -0000
*************** tree c_cont_label;
*** 131,136 ****
--- 131,139 ----

  static GTY(()) tree all_translation_units;

+ /* Outermost block. */
+ static GTY(()) tree ext_block;
+
  /* A list of decls to be made automatically visible in each file  
scope.  */
  static GTY(()) tree visible_builtins;

*************** c_write_global_declarations_1 (tree glob
*** 7570,7576 ****
  void
  c_write_global_declarations (void)
  {
!   tree ext_block, t;

    /* We don't want to do this if generating a PCH.  */
    if (pch_file)
--- 7573,7579 ----
  void
  c_write_global_declarations (void)
  {
!   tree t;

    /* We don't want to do this if generating a PCH.  */
    if (pch_file)
*************** c_write_global_declarations (void)
*** 7586,7591 ****
--- 7589,7598 ----
    external_scope = 0;
    gcc_assert (!current_scope);

+   /* We're done parsing; proceed to optimize and emit assembly.
+      FIXME: shouldn't be the front end's responsibility to call  
this.  */
+   cgraph_optimize ();
+
    /* Process all file scopes in this compilation, and the  
external_scope,
       through wrapup_global_declarations and  
check_global_declarations.  */
    for (t = all_translation_units; t; t = TREE_CHAIN (t))
*************** c_write_global_declarations (void)
*** 7608,7617 ****
       functions have magic names which are detected by collect2.  */
    build_cdtor ('I', static_ctors); static_ctors = 0;
    build_cdtor ('D', static_dtors); static_dtors = 0;
-
-   /* We're done parsing; proceed to optimize and emit assembly.
-      FIXME: shouldn't be the front end's responsibility to call  
this.  */
-   cgraph_optimize ();
  }

  #include "gt-c-decl.h"
--- 7615,7620 ----


-
Devang